Prime Minister Theresa May faces a crunch week for her leadership and Brexit plan, with ministers and backbenchers in her Conservative Party feuding over Britain’s future ties to the European Union.

May issued a plea for unity in an opinion piece in the Sunday Times newspaper, calling on Brexiters to “trust me to deliver.” “I will not let you down,” she wrote.

Less than a year until the U.K. leaves the EU, the government still hasn’t reached a consensus on what to seek in exit negotiations. Pro-Brexit ministers in May’s inner “war cabinet” -- which meets on Tuesday -- oppose her idea to maintain close customs relations with the bloc, a plan Foreign Secretary Boris Johnson labeled “crazy.” The Sunday Telegraph also reported that at least 12 members in the full cabinet of 28 are set to oppose it.

May last week ordered her ministers to take responsibility for resolving the issue themselves, splitting her inner cabinet into two working groups to iron out their differences.

Still Divided

There are two options under consideration. May’s preferred plan would see the U.K. mirror the EU’s customs regime, collecting EU tariffs and reimbursing businesses if U.K. tariffs are lower. A second plan, preferred by hard-line Brexit-backers, would set up a looser relationship and use technology to minimize disruption and border checks.

There was little sign of May’s strategy working on Sunday. Environment Secretary Michael Gove said on the BBC’s “Andrew Marr Show” that May’s plan had “flaws” and would see the U.K. acting as “tax collector” for the EU.

But the prime minister got a boost from pro-EU backbench lawmaker Kenneth Clarke, who told the BBC’s “Sunday Politics” that he may be willing to “settle” for her plan rather than holding out for full membership of the EU’s customs union.

The EU itself is also starting to engage with May’s proposal, having previously branded it unworkable. Echoing her language, Irish Deputy Prime Minister Simon Coveney told the BBC that May’s customs partnership could be the basis of negotiation as both sides seek to avoid a hard border. He dismissed the Brexiters’ preferred technology-based option.

May travels to Bulgaria this week for an EU summit, where she’s due to meet German Chancellor Angela Merkel and French President Emmanuel Macron for the first time since persuading them to join the U.K. in expelling Russian diplomats following the poisoning of a former spy in England in March.

The EU’s chief Brexit negotiator, Michel Barnier, is also scheduled to give a speech in Brussels Monday on post-Brexit foreign, security and defense policy.

Labour Split

Meanwhile, Brexit is also causing divisions in the main opposition Labour Party. Former leader Neil Kinnock wrote in the Independent newspaper that current chief Jeremy Corbyn would be guilty of a “serious evasion of duty” if he refused to back a plan to keep Britain in the European Economic Area after Brexit -- the so-called Norway option. Kinnock was writing after 83 Labour peers in the House of Lords voted in favor of EEA membership last week.

But Labour’s Brexit spokesman, Keir Starmer, said on the BBC’s “Andrew Marr Show” that the type of border infrastructure in place between Norway and Sweden would be unworkable at Ireland-Northern Ireland crossing points and therefore “was not the answer.”

Instead, Labour is seeking both a “comprehensive customs union” and a “strong single-market relationship that hardwires the benefits of the single market into the future agreement” with the EU, he said.

It’s the latest sign of the pressure building in the party to stay close to the EU after Brexit, after two senior Labour lawmakers told Bloomberg privately that they believed there was room for Corbyn’s position to shift.

A cross-party alliance of anti-Brexit lawmakers is also ratcheting up its efforts, now joined by former Labour Foreign Secretary David Miliband. Miliband, former Liberal Democrat leader Nick Clegg, and Conservative lawmaker Nicky Morgan wrote in the Mail on Sunday that Britain was being “held to ransom” by hardline Brexiters.

Writing in the Times, Prime Minister May requested the “help” of the British people and hinted that concessions would be needed.

“As in any negotiation, there will have to be compromises,” May wrote. “But if we stick to the task we will seize this once-in-a-generation opportunity to build a stronger, fairer Britain that is respected around the world and confident and united at home.”